Chapter 6

Summary		Questions		Media Resources
6.1 Biological membranes are fluid layers of lipid.
• Every cell is encased within a fluid bilayer sheet of phospholipid molecules called the plasma membrane.		1.  How would increasing the number of phospholipids with double bonds between carbon atoms in their tails affect the fluidity of a membrane?		•Membrane Structure
6.2 Proteins embedded within the plasma membrane determine its character.
• Proteins that are embedded within the plasma membrane have their hydrophobic regions exposed to the hydrophobic interior of the bilayer, and their hydrophilic regions exposed to the cytoplasm or the extracellular fluid. • Membrane proteins can transport materials into or out of the cell, they can mark the identity of the cell, or they can receive extracellular information.		2.  Describe the two basic types of structures that are characteristic of proteins that span membranes.		•Fluid Mosaic Model •Fluid Mosaic Model •Membrane Protein Diversity
6.3 Passive transport across membranes moves down the concentration gradient.
• Diffusion is the kinetic movement of molecules or ions from an area of high concentration to an area of low concentration. • Facilitated diffusion involves a protein carrier that transports molcules down their concentration gradients. • Osmosis is the diffusion of water. Because all organisms are composed of mostly water, maintaining osmotic balance is essential to life.		3.  If a cell's cytoplasm were hyperosmotic to the extracellular fluid, how would the concentration of solutes in the cytoplasm compare with that in the extracellular fluid?		•Diffusion •Osmosis •Diffusion •Osmosis •Activity: Diffusion •Activity: Osmosis • Understanding Membrane Transport • Osmotic Pressure
6.4 Bulk transport utilizes endocytosis.
• Materials or volumes of fluid that are too large to pass directly through the cell membrane can move into or out of cells through endocytosis or exocytosis, respectively. • In these processes, the cell expends energy to change the shape of its plasma membrane, allowing the cell to engulf materials into a temporary vesicle (endocytosis), or eject materials by fusing a filled vesicle with the plasma membrane (exocytosis).		4.  How do phagocytosis and pinocytosis differ? 5.  Describe the mechanism of receptor-mediated endocytosis.		•Exocystosis/endocytosis •Exocytosis/endocytosis •Activity: Bulk Passage Into and Out of the Cell
6.5 Active transport across membranes is powered by energy from ATP.
• Cells use active transport to move substances across the plasma membrane against their concentration gradients, either accumulating them within the cell or extruding them from the cell. Active transport requires energy from ATP, either directly or indirectly.		6.  In what two ways does facilitated diffusion differ from simple diffusion across a membrane? 7.  How does active transport differ from facilitated diffusion? How is it similar to facilitated diffusion?		• Exploration: Active Transport •Active Transport •Active Transport •Activity: Active Transport

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